Getting IPv6 connectivity on Ubuntu Linux is easy:
sudo apt-get install miredo
That's it! The "ifconfig' should now show a teredo interface with your 2001:-IPv6-address.
Surf to http://www.whatismyipv6.net/ to check your IPv6 connectivity and see your IPv6 address.
Or surf to http://ipv6.google.com/ : you should see the dancing Google logo.
BTW: miredo is the open source implementation of teredo.